The prostate cancer prevention trial risk calculator 2.0 performs equally for standard biopsy and MRI/US fusion-guided biopsy

Abstract

Background: The Prostate Cancer Prevention Trial Risk Calculator 2.0 (PCPTRC) is a widely used risk-based calculator used to assess a man's risk of prostate cancer (PCa) before biopsy. This risk calculator was created from data of a patient cohort undergoing a 6-core sextant biopsy, and subsequently validated in men undergoing 12-core systematic biopsy (SBx). The accuracy of the PCPTRC has not been studied in patients undergoing magnetic resonance imaging/ultrasound (MRI/US) fusion-guided biopsy (FBx). We sought to assess the performance of the PCPTRC for straitifying PCa risk in a FBx cohort.

Methods: A review of a prospective cohort undergoing MRI and FBx/SBx was conducted. Data from consecutive FBx/SBx were collected between August 2007 and February 2014, and PCPTRC scores using the PCPTRC2.0R-code were calculated. The risk of positive biopsy and high-grade cancer (Gleason ⩾7) on biopsy was calculated and compared with overall and high-grade cancer detection rates (CDRs). Receiver operating characteristic curves were generated and the areas under the curves (AUCs) were compared using DeLong's test.

Results: Of 595 men included in the study, PCa was detected in 39% (232) by SBx compared with 48% (287) on combined FBx/SBx biopsy. The PCPTRC AUCs for the CDR were similar (P=0.70) for SBx (0.69) and combined biopsy (0.70). For high-grade disease, AUCs for SBx (0.71) and combined biopsy (0.70) were slightly higher, but were not statistically different (P=0.55).

Conclusions: In an MRI-screened population of men undergoing FBx, PCPTRC continues to represent a practical method of accurately stratifying PCa risk.

Figure 1.

The calibration plots of the PCPTRC demonstrate the congruence between the estimated probabilities and the observed cancer rate. For the detection of any grade cancer, the mean absolute error was 0.026 with systematic biopsy and 0.025 with combined biopsy. For the detection of high-grade cancer with systematic biopsy, the PCPTRC over-predicted the observed high-grade cancer rate in the risk percentiles < 0.2 and > 0.5, with an absolute error of 0.047. In comparison, when detecting high-grade cancer with combined biopsy, the PCPTRC also tended to over-predict the actual rate of high-grade cancer within the risk percentiles < 0.2 and > 0.6. The mean absolute error was 0.48. Combined biopsy, combined targeted MRI/US fusion-guided biopsy with a 12-core systematic biopsy; MRI/US, magnetic resonance imaging/ultrasound; PCPTRC, cancer risk estimated by the Prostate Cancer Prevention Trial Risk Calculator 2.0; standard biopsy, standard 12-core biopsy.

Figure 2.

Area under the curve (AUC) of the receiver operator characteristics specify the ability of the PCPTRC to detect any grade cancer (above) and high-grade cancer (below) in combined biopsy and systematic biopsy. The ROC curve represents a graphical relationship between false-positive and true-positive rates. In the plots, a black line is tangentially drawn at a 45° angle to the ROC curve, demarcating a cutoff point, under the assumption that false negatives and false positives have equal value; the slope of the line can be used to calculate likelihood ratios for the test. ^aP = 0.55 comparing the AUC of systematic biopsy alone to combined biopsy. ^bP = 0.70 comparing the AUC of systematic biopsy alone to combined biopsy. Combined biopsy, combined targeted MRI/US fusion-guided biopsy with a 12-core systematic biopsy; MRI/US, magnetic resonance imaging/ultrasound; PCa, prostate cancer; PCPTRC, cancer risk estimated by the Prostate Cancer Prevention Trial Risk Calculator 2.0; ROC, receiver operator characteristic curves; standard biopsy, standard 12-core biopsy.